1. Field of the Invention
This invention relates to the measurement of electrical capacitance, as applied to the detection and measurement of dampness in structures. It relates in particular to the provision of an apparatus suitable for continuous determination of dampness over substantially flat surfaces such as roofs, floors, pavements and walls.
2. Description of Background Art
It is known to apply a pair of hand held probe type electrodes repeatedly to different locations over a surface to be tested, taking a reading of the capacitance or dampness at each application. Furthermore, existing moisture detectors depend upon changes in dielectric constant of the material in the fringe electrostatic field of coplanar electrodes. Such instruments have limited penetration depth because the fringe (or spray) electrostatic field falls off rapidly as the distance from the electrodes increases. Such instruments find useful applications in, for example, the paper manufacturing industry where the thickness of the paper is small However, for surfaces such as roofs where a penetration depth of several centimetres is required, fringe electrostatic field capacitance instruments do not perform satisfactorily. It is an object of the present invention to provide an apparatus which overcomes these problems.